1Low-x Meeting – Ischia Island, Italy – September 8 -13 2009

Diffractive quarkonium production in association with

a photon at the LHC*

Maria Beatriz Gay DucatiGFPAE – IF – UFRGSwww.if.ufrgs.br/gfpaebeatriz.gay@ufrgs.br

* Refer to work: arXiv:hep/0908.0507

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Outlook

Motivation Diffractive Physics Hadroproduction quarkonium + photon Pomeron Structure Function Multiple Pomeron Scattering Results Conclusions

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Motivation Higher statistics of small-x and hard diffractive processes

intensive experimental study

Has been used to improve the knowledge about QCD

Several mechanisms for quarkonium production in hadron colliders

Color singlet model

Color octet model1 Color evaporation model

Cross section for quarkonium production gluon densities

Pomeron with substructure gluons

Heavy quarkonium production clean signature through leptonic decay modes

1 J. P. Lansberg – Eur. Phys. J. C 60, 693 (2009)

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Introduction Diffractive processes overall cross sections

Regge Theory exchange of a Pomeron with vacuum quantum numbers

Nature of the Pomeron and its reaction mechanisms2 not completely known

Use of hard scattering quark and gluon content in the Pomeron

Observations of diffractive deep inelastic scattering (DDIS) at HERA (1994)

Increased the knowledge about the QCD Pomeron

Diffractive Distributions of singlet quarks and gluons in the Pomeron

2 P. D. Collins, An Introduction to Regge Theory and High Energy Physics (1977)

Diffractive structure function

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Diffractive events

Single diffraction in hadronic collisions one of the colliding hadrons emits Pomeron that scatters off the

other hadron

Hard diffractive events with a large momentum transfer

Absence of hadronic energy in certain angular regions of the final state phase space

Rapidity gaps

Central diffractive events

Both colliding hadrons remain intacts as they emit a Pomeron each

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Diffractive Physics

2

2X

IP W+Q

tM+Q=x

2

2

β=Q2

Q2+M X2 −t

=x

x IP

Ingelman-Schlein Model

2)p(p=t '

Momentum fraction of partons inner the Pomeron

Squared of the proton's four-momentum transfer

Momentum fraction of the proton carried by the Pomeron

3

3 G. Ingelman and P. Schlein, Phys. Lett. 152B (1985) 256.

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o Focus on the following single diffractive processes

Diffractive hadroproduction

o Diffractive ratios as a function of transverse momentum pT of quarkonium state

o Quarkonia produced with large pT easy to detect

X+γ+ψJ+ppp / X+γ+Υ+ppp

o Singlet contribution

o Octet contributions

o Higher contribution on high pT 4

4 J. P. Lansberg, arXiv:hep-ph/0901.4777

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J/ψ+γ production

Considering the Non-relativistic Quantum Chromodynamics (NRQCD)

Gluons fusion dominates over quarks annihilation 4

Leading Order cross section convolution of the partonic cross section with the PDF

MRST 2001 LO no relevant difference using MRST 2002 LO and MRST 2003 LO

Non-perturbative aspects of quarkonium production

4 J. P. Lansberg, arXiv:hep-ph/0901.4777

v is the relative velocity of the quarks in the quarkonia

• Expansion in powers of v

NLO expansions in αs one virtual correction

and three real corrections

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Quarkonium + photon production

Singlet subprocess

Octet subprocess,

5

5 C. S. Kim, J. Lee and H. S. Song, Phys. Rev. D55 (1997) 5429

No gluon interactions

Gluon interactions

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NRQCD Factorization

Negligible contribution of quarks annihilation at high energies6

6 R. Li and J. X. Wang, Phys. Lett. B672 (2009) 51

is the center mass energy (LHC = 14 TeV )

J/ψ rapidity

9.2 GeV2

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( ) is the momentum fraction of the proton carried by the gluon

NRQCD factorization

Cross section written as

invariant mass of J/+ system

Coefficients are computable in perturbation theory

Matrix elements of NRQCD operators

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Matrix elements

Bilinear in heavy quarks fields which create as a pair Q Q Quarkonium state 7

7 T. Mehen, Phys. Rev. D55 (1997) 4338

ec=23

αs running

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Matrix elements (GeV3)

1.16

1.19 x 10-2

0.01

0.01 x m2c

10.9

0.02

0.136

0

8, 9

8 E. Braaten, S. Fleming, A. K. Leibovich, Phys. Rev. D63 (2001) 0940069 F. Maltoni et al., Phys. Lett. B638 (2006) 202

eb=−13

5.4=mb

46.9=m GeV/c2

GeV

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Diffractive cross section

Momentum fraction carried by the Pomeron

Squared of the proton's four-momentum transfer

Pomeron flux factor

Pomeron trajectory

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Variables to DDIS

Q 02= 2 . 5 G eV 2

Cuts for the integration over xIP

Λ QCD=0 . 2 4

22

2ψT

F

m+p=μ

Scales

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Pomeron structure functionParametrization of the pomeron flux factor and structure function

10 H1 Coll. A. Aktas et al, Eur. J. Phys. J. C48 (2006) 715

Normalization parameter

mp = proton mass

Parameter Value

α’IP

BIP

αIR(0)

α’IR

BIR

mc

mb

α8 (5) (MZ

2)

2+ GeV

0.190.060.06

2+ GeV

2.00.75.5

0 . 50±0 . 102+ GeV

0.60.30.3

2+ GeV

1.60.41.6

1. 4±0 . 2 GeV

4,5±0 . 5GeV

0 . 118±0 . 002

Normalized for

H1 Collaboration 10

Low-x Meeting – Ischia Island, Italy – September 8 -13 2009

Gluon distribution

• Range 0.0043 < z < 0.8

• Same of experiment

• In this work we use FIT A.

• Similar results with FIT B

Fit A (and uncertainties) color center line

Fit B (and uncertainties) black line

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Gap

• Described in terms of screening or absortive

corrections

•Multiple Pomeron effects absorptive

corrections

• <|S|2> gap survival probability (GSP)

•

• A(s,b) amplitude of the particular diffractive process of interest

• PS(s,b) probability that no inelastic interactions occur between

scattering hadrons

Gap Survival Probability (GSP)

22

22

2

|b)A(s,|bd

s)(b,P|b)A(s,|bd|>S|

s

11 E. Gotsman, E. Levin, U. Maor and A. Prygarin, arXiv:hep-ph/0511060

11

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KKMR model

• Pion-loop insertions in the bare Pomeron pole nearest singularity

generated by t-channel

unitarity

• Two-channel eikonal incorporates Pomeron cuts generated by

elastic and quasi-elastic s-channel unitarity

• High-mass diffractive dissociation

Multiple Pomeron effects absorptive corrections

• Good description of the data of the total and differential elastic cross section

• Value of <|S|2> = 0.06 at LHC single diffractive events

11 E. Gotsman, E. Levin, U. Maor and A. Prygarin, arXiv:hep-ph/0511060

11KKMR description to hadronic collisions embodies:

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Results to J/+

• Predictions for inclusive and diffractive cross sections

• RHIC, Tevatron and LHC

• Diffractive cross sections considering GSP (<|S|2>)

• Reproduces descriptions of 5

-1 < |y| < 1

• B = 0.0594 is the branching ratio into electrons

5 C. S. Kim, J. Lee and H. S. Song, Phys. Rev. D55 (1997) 5429

201 Tp at LHC12

12 Renu Bala, XLVII International Winter Meeting on Nuclear Physics (2009)

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Results to J/+ at LHC • B = 0.0594

• Absolute value of inclusive cross section strongly dependent

• Diffractive cross sections (DCS) without GSP

• Comparison between two different sets of diffractive gluon distribution (H1)

• Absolute value of DCS

weakly sensitive to the uncertainties of DPDF

o Quark mass

o NRQCD matrix elements

o Factorization scale

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Results to Υ+

• Predictions of inclusive cross section

• RHIC, Tevatron and LHC

-1 < |y| < 1

• B = 0.0238 is the branching ratio into electrons

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Results to Υ+ at LHC • B = 0.0238

• Absolute value of inclusive cross section strongly dependent

• Diffractive cross sections (DCS) without GSP (<|S|2>)

• Comparison between two different sets of diffractive gluon distribution (H1)

• Dependence of FITs are slight more pronounced in charmonium case

o Quark mass

o NRQCD matrix elements

o Factorization scale

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Diffractive ratio

Slight large diffractive ratio

in comparison to 5

[σ] = pb

considering FIT A

5 C. S. Kim, J. Lee and H. S. Song, Phys. Rev. D55 (1997) 5429

This work Ref 5

<|S|2>=0.06 Renormalized Pomeron flux

Evolution of Q2 in gluon density

No evolution of Q2

4

2 2ψT

F

m+p=μ

Could explain the pT dependence

in our results

TF E=μ

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Conclusions• Theoretical prediction for inclusive and single diffractive quarkonium +

photon production at LHC energy in pp collisions

• Estimates for differential cross sections as a function of quarkonium transverse momentum

• Diffractive ratio is computed using hard diffractive factorization and absorptive corrections

• Ratios are less dependent on the heavy quarkonium production mechanism

• Quite sensitive to the absolute value of absorptive corrections

• Distribution on

• Next step Next-to-Leading Order

R(J/ψ)SD = 0,8 – 0,5 %

R(Υ)SD = 0,6 – 0,4 %

104 Tp